Traditionally, due to a limit of a Selective Availability (SA) policy of the United States, positioning accuracy of a Global Positioning System (GPS) unlicensed by the government of the United States may be reduced. Specifically, a plane position error is smaller than 100 m and an elevation error is smaller than 1.56 m. After the SA policy is abolished, single-point positioning accuracy of the GPS is improved to a certain extent. However, the improved accuracy can reach 20 to 40 m only, and positioning accuracy of a Beidou positioning system is also at a similar order of magnitude. Such accuracy levels are unlikely to meet accuracy requirements of some application fields, for example, aircraft landing, ship entry and Internet of vehicles scheduling.
Recently, the industry proposed use of a GPS/Beidou differential positioning method for improvement of positioning accuracy, and positioning accuracy in part of scenarios may reach a meter level or even a centimeter level. There are usually three differential positioning methods, i.e., wide area differential, single-station differential and areal differential methods.
Specifically, the wide area differential method separates and estimates various errors through a positioning server and performs single-point positioning by virtue of more accurate satellite ephemeris, satellite clock error correction and atmospheric delay model to improve positioning accuracy, and a positioning error is substantially unrelated to a distance between a user and a reference station. However, the wide area differential method is technically complex, need a large construction investment and a long period and involves more industries and departments. In addition, disseminating differential information by virtue of an idle channel of a broadcast signal also requires a terminal to be added with a receiver and a corresponding software parsing function, so that the method is inapplicable to heavily demanded positioning service.
The single-station differential method is simple in structure and algorithm, technically mature and applicable to differential positioning work within a small range. However, during single-station differential, the terminal may receive a correction signal of only one reference station, so that system reliability is poorer. Correspondingly, after the reference station fails, no positioning service may be provided.
The areal differential method involves multiple reference stations and considers influence of a position on differential correction, so that both overall system reliability and the positioning accuracy of the user are greatly improved. However, like the single-station differential method, influence caused by various error sources is combined for consideration in a processing process, and when distances between the reference stations and the terminal are longer, errors are greater and accuracy is lower.
On one hand, the existing differential positioning methods all require additional transmission of “positioning correction information” with a communication link of the terminal, so that cost and complexity of the terminal are increased. On the other hand, a large number of positioning reference stations are required to be constructed, so that construction and maintenance cost is greatly increased.
In the mobile Internet era, both merchants and users require more accurate and timely position information to obtain more business opportunities or more detailed custom service. Along with continuous development of the Internet of vehicles, a requirement on accurate positioning will further be increased in the future, and an assistant high-accuracy positioning service may become an important application with a high frequency of occurrence for users of the whole network in the future.